Determination of point proton radii of neutron-rich carbon isotopes

Abstract

Exotic features like the halo and the (dis)appearance of the magic numbers were revealed by investigating the nuclei towards the neutron-rich region that have a large neutron/proton asymmetry. Investigating the evolution of proton radii together with the matter radii along an isotopic chain will allow us to characterize the halo formation, neutron skin thickness, and shell evolution around the neutron drip-line. The first determination of the point proton radii of neutron-rich carbon isotopes ^20,22C is presented in this work. The proton radii of these neutron-rich carbon isotopes were determined from a measurement of the charge-changing cross-section &sigma;_cc, defined as the sum of cross sections of reactions that changes the atomic-number (<em>Z</em>). The experiment was performed at the BigRIPS facility at RIKEN Nishina Center in Japan, at a relativistic beam energy around &sim; 200<em>A</em> MeV with a carbon target. The proton radii were extracted from the measured &sigma;_cc using the nite range Glauber model framework. The proton radii increase for ²⁰C and ²²C compared to the previously measured carbon isotopes ^12&minus;19C, showing signatures of the disappearance of shell closures at <em>N</em> =14 and <em>N</em> = 16 along this isotopic chain. The neutron skin thickness (∆<em>R</em>_np) of these neutron-rich carbon isotopes (^{20,<em>22</em>}C) is reported for the rst time in this thesis using the proton radii determined in this work and measured matter radii available from the literature. ∆<em>R</em>_np of 1.23 (20) fm is determined for the two-neutron halo, ²²C affirming the presence of a halo. The halo radius of 6.6 &plusmn; 1.1 fm in ²²C is found to be as large as ¹¹Li. The proton radii are compared to the predictions reported for these neutron-rich carbon isotopes. The experimental proton radii have challenged these predictions.